Rollie.
I know all the questions you have, and the confusing answers you are getting. I see it all most every day with customers. I sell campers and have had trucks with campers over the years. If you have an extended cab it is going to haul 3000 lbs a whole lot better than a regular cab truck. This is because the longer wheel base allows more of the camper weight to be distributed to the front axles. By transfering the weight off the rear of the truck you are also taking some weight off the tires. I saw this 1st hand a few years ago when I sold a Lance I had owned for a few years. Originally it was installed on my 97 F350 regular cab longbed. The camper severely put the back of the truck down. By putting airbags on that truck, that brought the back up level but still left all that weight right over the rear axle bulging the rear tires (load range E's) badly. The truck went away and that's when I got into Dodges. Anyway, when I sold that camper I sold it to a person who had a crew cab (longer wheel base) F350 with the same "GVW" rating as what my Ford was. When we set that same 10' camper in the back of that crew cab his truck sat level. I saw 1st hand what a diference that ;longer wheel base did.
The thing that adds to confusion is that a regular cab (on paper) is rated to carry more weight than an extended cab or crew cab. That is because of the added seat belts. Sure that extra weight of the frame and body will deduct from the gross payload but the government mandated another 150 per seatbelt be deducted from the gross payload as well. I tell people if they are not filling those seatbelts, put that weight back into what they want to carry. Another thing to consider is the manufacturer. Dodge suspensions, 3/4 and 1 ton trucks have the best springs to handle the weight of a camper. They handle the weight better than Ford or Chevy. That opinion comes from seeing the same campers on a daily basis in the different trucks. Hope this helps you I could go on and on. One thing I strongly suggest is the Rancho 9000's. If you have an extended cab truck with the camper package; sway bar and overload spring you won't have any problems with 3000 lbs or under. Be sure of the exact weight of the camper you are going to buy. Manufacturers usually list wet weights on campers that only include the standard equipment for that particular model. One thing I strongly reccommend is the Rancho 9000's. They will make a BIG
difference in the way your truck handles the weight. WyoJim wrote of this.
Good Luck.